1. Technical Field
The present invention relates to a radiation detector and, more particularly, to an amplifier for converting a charge signal output from a radiation detecting element into a voltage signal and to a radiation detector including the amplifier.
2. Description of Related Art
A radiation detector for detecting radiation such as X-rays includes a radiation detecting element such as a SDD (Silicon Drift Detector). The radiation detecting element outputs a charge signal in accordance with energy of the detected radiation. The charge signal is converted into a voltage signal by a preamplifier. The voltage signal is further amplified, and signal processing such as generating a spectrum is performed based on the amplified voltage signal.
FIG. 1 is a circuit diagram of a preamplifier in the conventional radiation detector. Each of a capacitor 33 for feedback (hereinafter also referred to as a feedback capacitor) and a normally-open switch 34 is connected in parallel to an amplifying circuit 31. Each time the charge signal is input from the radiation detecting element to the preamplifier, the charge is stored in a capacitor 33 and thus a value of the voltage signal output from the preamplifier continues to increase. Therefore, the capacitor 33 needs to be reset to discharge the stored charge by closing the switch 34 when the voltage signal reaches a predetermined value. However, resetting causes dead time during which radiation cannot be detected. To shorten dead time, the reset time (the time required to reset) needs to be shortened. Japanese Patent Application Laid-Open No. 2011-4326 discloses a technique for shortening the reset time in the amplifying circuit.